linux-kernel - Re: [PATCH] mm/memblock.c: make the index explicit argument of for_each_memblock

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Date:   Wed, 13 Sep 2017 13:05:02 +0200
From:   Gi-Oh Kim <gi-oh.kim@...fitbricks.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org
Subject: Re: [PATCH] mm/memblock.c: make the index explicit argument of for_each_memblock_type

On Wed, Sep 13, 2017 at 12:55 PM, Michal Hocko <mhocko@...nel.org> wrote:
> On Wed 13-09-17 11:06:06, Gioh Kim wrote:
>> for_each_memblock_type macro function uses idx variable that is
>> the local variable of caller. This patch makes for_each_memblock_type
>> use only its own arguments.
>
> strictly speaking this changelog doesn't explain _why_ the original code
> is wrong/suboptimal and why you are changing that. I would use the
> folloging
>
> "
> for_each_memblock_type macro function relies on idx variable defined in
> the caller context. Silent macro arguments are almost always wrong thing
> to do. They make code harder to read and easier to get wrong. Let's
> use an explicit iterator parameter for for_each_memblock_type and make
> the code more obious. This patch is a mere cleanup and it shouldn't
> introduce any functional change.
> "

Absolutely this changelog is better.
Should I send the patch with your changelog again?
Or could you just replace my changelog with yours?

>
>> Signed-off-by: Gioh Kim <gi-oh.kim@...fitbricks.com>
>
> Acked-by: Michal Hocko <mhocko@...e.com>
>
>> ---
>>  include/linux/memblock.h | 8 ++++----
>>  mm/memblock.c            | 8 ++++----
>>  2 files changed, 8 insertions(+), 8 deletions(-)
>>
>> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>> index bae11c7e7bf3..ce0e5634c2f9 100644
>> --- a/include/linux/memblock.h
>> +++ b/include/linux/memblock.h
>> @@ -389,10 +389,10 @@ static inline unsigned long memblock_region_reserved_end_pfn(const struct memblo
>>            region < (memblock.memblock_type.regions + memblock.memblock_type.cnt);    \
>>            region++)
>>
>> -#define for_each_memblock_type(memblock_type, rgn)                   \
>> -     for (idx = 0, rgn = &memblock_type->regions[0];                 \
>> -          idx < memblock_type->cnt;                                  \
>> -          idx++, rgn = &memblock_type->regions[idx])
>> +#define for_each_memblock_type(i, memblock_type, rgn)                        \
>> +     for (i = 0, rgn = &memblock_type->regions[0];                   \
>> +          i < memblock_type->cnt;                                    \
>> +          i++, rgn = &memblock_type->regions[i])
>>
>>  #ifdef CONFIG_MEMTEST
>>  extern void early_memtest(phys_addr_t start, phys_addr_t end);
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index 91205780e6b1..18dbb69086bc 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -533,7 +533,7 @@ int __init_memblock memblock_add_range(struct memblock_type *type,
>>       base = obase;
>>       nr_new = 0;
>>
>> -     for_each_memblock_type(type, rgn) {
>> +     for_each_memblock_type(idx, type, rgn) {
>>               phys_addr_t rbase = rgn->base;
>>               phys_addr_t rend = rbase + rgn->size;
>>
>> @@ -637,7 +637,7 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
>>               if (memblock_double_array(type, base, size) < 0)
>>                       return -ENOMEM;
>>
>> -     for_each_memblock_type(type, rgn) {
>> +     for_each_memblock_type(idx, type, rgn) {
>>               phys_addr_t rbase = rgn->base;
>>               phys_addr_t rend = rbase + rgn->size;
>>
>> @@ -1715,7 +1715,7 @@ static void __init_memblock memblock_dump(struct memblock_type *type)
>>
>>       pr_info(" %s.cnt  = 0x%lx\n", type->name, type->cnt);
>>
>> -     for_each_memblock_type(type, rgn) {
>> +     for_each_memblock_type(idx, type, rgn) {
>>               char nid_buf[32] = "";
>>
>>               base = rgn->base;
>> @@ -1739,7 +1739,7 @@ memblock_reserved_memory_within(phys_addr_t start_addr, phys_addr_t end_addr)
>>       unsigned long size = 0;
>>       int idx;
>>
>> -     for_each_memblock_type((&memblock.reserved), rgn) {
>> +     for_each_memblock_type(idx, (&memblock.reserved), rgn) {
>>               phys_addr_t start, end;
>>
>>               if (rgn->base + rgn->size < start_addr)
>> --
>> 2.11.0
>>
>
> --
> Michal Hocko
> SUSE Labs



-- 
Best regards,
Gi-Oh Kim
TEL: 0176 2697 8962